Extreme temperatures affect seedling growth and photosynthetic performance of advanced cotton genotypes

Abstract Growth temperature and genotype can influence seedling vigor in cotton (Gossypium hirsutum L.), and identifying genotypes that can perform well under different temperature extremes may broaden the range of temperatures over which optimum growth could be obtained. To this end, a controlled environment study was conducted to evaluate the response of advanced breeding lines to growth temperature and to evaluate the utility of rapid, fluorescence-based measurements (the OJIP test) as indicators of plant growth response to day/night temperature regimes (20/15, 30/20, 35/25, and 40/30 °C). At two weeks after planting, growth analysis, chlorophyll fluorescence measurements, and pigment concentrations were obtained. Significant genotype, temperature, and interaction effects were observed for seedling growth parameters, and some of the key components of the thylakoid reactions. Specifically, the 35/25 °C treatment had the highest values for all growth parameters, with genotypic differences in growth primarily being observed at this regime. Energy trapping by photosystem II (PSII) (φPO), intersystem electron transport (φEO), and photosystem I end electron acceptor reduction (φRO) were significantly affected by temperature, but each component differed in heat sensitivity. All growth parameters were significantly correlated with a number of OJIP parameters including quantum efficiencies and performance indices. However, the strongest positive associations were observed between quantum efficiencies and growth metrics, with φEO exhibiting the strongest correlations with growth. Our observations indicate that rapid OJIP assessments can potentially be used as indicators of early season growth responses to temperature.